1. Technical Field
The present invention relates to wireless communications and, more particularly, wideband wireless communication systems.
2. Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards, including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc., communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of a plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via a public switch telephone network (PSTN), via the Internet, and/or via some other wide area network.
Each wireless communication device includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives an inbound RF signal via the antenna and amplifies it. The one or more intermediate frequency stages mix the amplified RF signal with one or more local oscillations to convert the amplified RF signal into a baseband signal or an intermediate frequency (IF) signal. As used herein, the term “low IF” refers to both baseband and intermediate frequency signals. A filtering stage filters the low IF signals to attenuate unwanted out of band signals to produce a filtered signal. The data recovery stage demodulates the filtered signal to recover the raw data in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier stage. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier stage amplifies the RF signals prior to transmission via an antenna. In certain RF transceivers, the transmitter may be implemented as a translational loop transmitter.
A translational loop transmitter may include a digital processor, digital to analog converter (DAC), low pass filter, and a phase locked loop (PLL). The digital processor, in general, produces a digital version of the desired RF spectrum at some intermediate frequency (e.g., 26 MHz for GSM). The DAC converts the digital signals into the analog domain, which are subsequently filtered by the low pass filter. The translational loop translates the frequency of the analog signals outputted by the low pass filter to the desired radio frequencies. Specifically, a mixer in the feedback path of the translational loop uses an RF reference signal provided by a PLL frequency synthesizer to perform this “translation” of the IF signal to the desired RF frequency.
Thus, in a typical conventional RF transceiver architecture, the transmitter is designed around a translational loop where a separate PLL frequency synthesizer provides an RF frequency signal to the translational loop. In the receive mode, the PLL frequency synthesizer provides the RF frequency to the receiver. However, translational loops are expensive, consume large amounts of power and occupy a large amount of die space in RF transceivers. Therefore, what is needed is a low power and minimum cost RF transceiver architecture that operates using a conventional PLL frequency synthesizer in both a transmitting mode for generating the transmitted signals and a receiving mode for generating the local oscillations mixed with the received signals.